The present invention relates to a process for recovering a heavy metal catalyst component from a waste catalyst. Generally in chemical industries, especially in the petrochemical industry, petroleum refining industry and the soap and detergent industry, a great amount of heavy metal catalysts such as Ni, Co, Mo, V, Cu and the like are used. Such catalysts are used, for example, in the production of various synthetic polymers, desulfurization of petroleum, hydrogeneration of oils and/or fats, etc. Most of these catalysts are employed in a form of so-called supported catalysts wherein the heavy metal is deposited on the surface of the support or carrier composed of a porous, noncombustible inorganic material such as Al.sub.2 O.sub.3, SiO.sub.2, MgO, CaO, ZrO.sub.2 and the like. Recently, the amount of these catalysts consumed has been rapidly increasing with the remarkable growth of the above said industries. Therefore, there exists a need to develop an economical process for completely recovering the heavy metal catalytic component from the waste catalyst. Since the waste catalysts are continually spent in great quantities, they represent a potential cause of environmental pollution. In one prior art process, the heavy metal from the spent catalyst is utilized as a component in the production alloys, wherein the waste catalyst containing an analytically determined amount of the heavy metal is added to a metal previously melted in an electric furnace. However, since the amount of the waste catalyst which can be added is limited as compared with that of the metal of the original melt, this method is not suitable for continuously treating a great amount of waste catalyst. Further, this method has the disadvantage of lowering the efficiency of the alloy production process by producing an enormous volume of slag.
In another prior art process, a nickel containing waste catalyst used in the hydrogenation of oils and/or fats is agitated in an organic solvent such as acetone to separate oils and/or fats. Nickel and kieselguhr, enabling reuse of these components. However, since it is difficult in this process to separate each component completely, large scale treatment is not attainable and the cost is prohibitedly expensive. This method also has the disadvantage of requiring an immense expense for preventing secondary environmental pollution caused by the waste water generated in the process.
U.S. Pat. No. 3,577,217 discloses another prior art process wherein a spent catalyst represented by the formula CuO-CuCr.sub.2 O.sub.4 is heated in admixture with a carbonate or hydroxide of an alkali metal in the presence of oxygen and then the resulting reaction mixture is mixed with water to recover cupric oxide as an insoluble solid and a chromic acid salt of the alkali metal in the aqueous solution. However, it is difficult in the above process to separate and recover the support, and therefore, it is inapplicable to the recovery of the heavy metals from spent supported catalysts.
U.S. Pat. No. 4,029,495 to Hirayama discloses a process for recovery of heavy metals from spent catalyst materials. The Hirayama process comprises introducing the spent supported catalyst in the form of a powder into a rotary, rocking or gradient furnace, heating the spent catalyst in the furnace to a temperature of at least a 1000.degree. C. to transform it into a sintered or seim-melted state, agitating the sintered or semi-melted mass to cause the metallic particles to aggregate as discrete masses and further cause the sintered mass to break up or granulate and separating the metallic catalytic component from the other components. Hirayama also contemplates use of the catalytic carrier support material in a process for formation of ceramic fibers of alumina and silicate. This method suffers from the disadvantages that the adjustment of composition of the alumina carrier material prior to formation into the fibers is difficult without contaminating the heavy metal being recovered and further the process is one embodiment uses a great deal of energy which is lost by cooling of the material for separation of the metallic component from the other components.
U.S. Pat. No. 4,142,871 to Zeiringer discloses a process for recovery of heavy metals from spent catalytic material. The Zeiringer process comprises the steps of melting the catalytic starting material with a reducing agent to obtain a melt consisting of a melt component including the alumina on an alloy residue, cooling the melt at a speed collated with the desired crystalite size of the abrasive material to be obtained and mechanically separating the melt component from the alloy residue before or after solidification. The melt component is used as an abrasive material. This process has the disadvantage that the adjustment of the abrasive material composition is difficult in the presence of the heavy metal which is to be recovered. Further, the process wherein the material is cooled prior to separation makes difficult the recycling of materials.
Therefore, there remains a need for an improved method of efficiently separating heavy metal materials from spent catalyst materials.